Interpretive Summary: Zebra chip, a newly emerging and economically important potato disease in the United States, Mexico, Central America, and New Zealand, is caused by a previously undescribed species of the bacterium liberibacter vectored by the potato psyllid. Researchers at USDA-ARS Yakima Agricultural Research Laboratory, Wapato, WA evaluated effects of environmental factors on development of this plant pathogen and the potato disease. It was discovered that high temperatures during the potato growing season prevent development of this bacterium and zebra chip disease. Information from this research will help potato producers and scientists predict incidence and severity of the disease in affected regions depending on climatic conditions.

Technical Abstract:
Temperature has been shown to have significant impact on development of liberibacter species associated with citrus Huanglongbing disease. “Candidatus Liberibacter africanus” and “Ca. L. americanus” are both heat sensitive, whereas “Ca. L. asiaticus” is heat tolerant. The recently described “Ca. L. solanacearum” is associated with zebra chip (ZC), a newly emerging and economically important disease of potato worldwide. This psyllid-transmitted liberibacter species severely affects several other solanaceous crops and carrot. Experiments were conducted to evaluate effects of temperature on development of “Ca. L. solanacearum” and ZC disease. Potato plants were inoculated with “Ca. L. solanacearum” by briefly exposing them to liberibacter-infective potato psyllids at various temperatures under laboratory conditions. Following insect exposure, the plants were maintained at selected temperature regimes in growth chambers and monitored for ZC symptom development and later tested for liberibacter by polymerase chain reaction to confirm infection. Results indicated that temperatures below 17 °C appear to slow development of “Ca. L. solanacearum” and ZC symptoms whereas temperatures above 35 °C are detrimental to this liberibacter. Compared to Huanglongbing liberibacters, “Ca. L. solanacearum” appears heat tolerant. This sensitivity of this bacterium and its insect vector to temperature may partially explain incidence, severity, and distribution of ZC in affected regions.